CCTV footage of the alleged offender. Photo: Supplied

The victim of a cowardly punch that resulted in a fractured skull in central Christchurch is now conscious.

Leni Taufateau was knocked to the ground on Oxford Tce about 1am on Sunday.

The promising 19-year-old rugby player suffered serious injuries after the incident.

Police say the attacker was a member of a Mongrel Mob group in the city for the weekend.

Detective Senior Sergeant Nicola Reeves said a man punched another man, causing the victim to fall to the ground and hit his head on the pavement.

"The victim became unconscious and was transported to hospital where he remains," Reeves said.

"The offender was one of a group of Mongrel Mob who were socialising in town at the time and is described as Māori with tattoos on his arms, wearing black clothing, a black hat and a red bandanna wrapped around his wrist."

Police are appealing to the public for information to help find the offender.

"Anyone who has information about the assault is encouraged to contact police on 105 quoting file number 210131/5776 or anonymously on 0800 Crimestoppers."